Hydraulic casing systems in mine workings

ABSTRACT

This invention provides a hydraulic casing system comprising automatically advancing casing structures which are connected together in groups in such fashion that in each group only one casing structure can move at once, although several casing structures in different groups can move at the same time, the casing structures being allocated individual control systems which are prepared for the advancing movement, or are locked, by elements which sense a freedom to advance, in particular by sensing elements which cooperate with the roof or sill of the seam or working, and is characterized by the fact that the individual control systems are incorporated in a logic system governing the selective advance of the different groups.

limited tats tat Schmidt [54] HYDRAULIC CASKNG SYSTEMS IN FOREIGNPATENTS OR APPLICATIONS MHNE WURMNW 1,313,793 11/1962 France 137/111[72] Inventor: llllelmut Schmidt, Essen-Haarzopf, Ger- 877,995 1961Great 61/ 52 many 1,043,846 9/1966 Great Britain... ..137/1 12 19 [73]Assignee: Hergwerltsverhand Gmblll, Essen, Gerl 079 172 8/ 67 Great Bmam61/45 2 y OTHER PUBLlCATllONS 1 Filedi J1me 1968 Process Control andAutomation, July, 1964, Universal [211 APPL 736,487 Modular System forPneumatic Switching Controls, Ab-

stractecl by L. A. Stemer, pp. 310 312.

1 Foreign Application Priwily Dam Primary Examiner-Martin P. SchwadronAssistant Examiner lrwin C. Cohen J 14, 1967 G ..P 15 33 723.2

une ermany Att0rneyMalc0lm W. Fraser [52] 1U.S.C1. ..61/45D,91/1,91/189,

[51] Int. Cl. .EZIC 35/24, FlSb 1 H16, F1513 13/06 This inventionprovides a hydraulic casing System comprising [58] lFteld of fiearclh..91/35, 170 MP, 189,412; 1/36; automatically advancing casing Sructureswhich are com 61/45'2 nected together in groups in such fashion that ineach group only one casing structure can move at once, although several15 6] References Cmd casing structures in different groups can move atthe same UNITED STATES PATENTS time, the casing structures beingallocated individual control systems which are prepared for theadvancing movement, or 3,495,499 2/1970 Ward ..91/189 X are locked, byelements which sense a freedom to advance, in 3,207,041 9/1965 Phillips....9l/1 X particular by sensing elements which cooperate with the roof3,259,024 7/1966 Klbble a] 1 1 or sill of the seam or working, and ischaracterized by the fact 3,285,015 11/196 Carnegle et 91/170 MP thatthe individual control systems are incorporated in a logic 3,303,9992/1967 137/625-66 X system governing the selective advance of thedifferent 3,348,381 10/1967 Jacobi.. groups 3,392,532 7/1968 Jacobi3,405,608 10/ 1968 Teale. 6 Claims, 4 Drawing Figures i101 502 ljjm my;505 506 507 GB 509 I 1 1 1 1170 12171: c 11711 1 2171: 317b 6 "Te 26I2|7c 3'6 1 3m) 116a I 2160 316a I 11Gb 2|6h 1 31Gb 11 c l 1 c l 1 c I114 21 3140 Hill 213 313 113 213 514 30 2130 33a 33b 5131: 33b 53: BM313a 1 1 1 1 1 l 1 1 1 I l l E 2151 3 1 1 i 21 2 1 m 1 l l l I l 1 l l ll 1 194u 340 i040 1041: 3041: 34b 34c 2041: i041;

PATENTEDFEB22 1912 3.643 ,445

sum 3 or 4 79 4/MZQ/MMI HYDRAULIC CASING SYSTEMS IN MINE WOlRlKllNGSBACKGROUND OF THE INVENTION I. Field of the Invention The control of ahydraulic casing system is intended on the one hand to ensure thatsupport is not removed from the roof of the seam simultaneously by twoor more neighboring casing structures, and on the other hand that theroof exposed by any advance, equivalent to the length of a full step orfraction thereof on the part of a casing structure, is immediatelyunderpinned by the casing structure in question. It is only in this waythat maximum safety of working can be achieved.

2. Prior Art The group arrangement, within control systems of this kind,is a well known one. It has the advantage that several casing structurescan feed forward simultaneously at the seam so that the rate of advanceof the structures is increased and the roof of the working more rapidlyunderpinned than when using other control systems in which only onestructure can advance at a time. In addition, it is also known toimprove the operation of the casing systems by arranging for thestructures to advance automatically, the group-associated controlsystems being for example independent units, so that as a result all thecasing structures advance until the whole of the exposed roof zones ofthe working are cased. Then the casing is effective even when the seamis not being worked.

In the known automatic control systems, it has to be arranged that acasing structure which is not advancing prevents the transmission of anadvancing or feed signal to a neighboring casing frame. To this end, inaccordance with another of the known control systems, a stepping switchmechanism is employed as the group-associated control system, thismechanism applying a feed signal of specific duration and in a specificsequence to the control systems associated with each casing structure,and thus in effect sampling these structures so that a given casingstructure either advances or remains stationary without impeding theadvancing movement of neighboring casing structures. This steppingswitch mechanism however, cannot for practical reasons be synchronizedto prevent simultaneous feeding forward of neighboring casing structuresrespectively belonging to separate groups (i.e., at the junctionsbetween groups). However, this kind of possibility must be excluded forsafety reasons.

Another disadvantage ofthese control systems resides in the fact thatthe groups, of necessity, and not least in respect of the problemsoccurring at the junctions between them, have to be relativelyextensive, i.e., have to cover more than three casing frames.Accordingly, the casing of roof areas which have suddenly been exposed(for example as a consequence of the collapse of extensive lengths ofcoal seam where there are no it-props at the working face) takes toolong.

OBJECT OF THE INVENTION The problem with which the present invention isconcerned is that of avoiding these drawbacks.

BRIEF SUMMARY OF THE INVENTION The invention sets about resolving thisproblem by arranging for all the control systems associated with thevarious casing structures to be grouped into a logic system, and bylocking each casing structure with at least two of the neighboringcasing structures to form alternating groups.

By means of the invention, the earlier division of the casing systeminto fixed groups, i.e., permanently fixed, or fixed for protractedperiods, in terms of their location in the seam, is obviated. Instead,due to the logic system, alternating groups (as far as their location inthe seam is concerned and in terms of their readiness for advancing) arecreated and the number of casing structures within these alternatinggroups becomes an arbitrary matter and is determined in accordance withparticular mining requirements, i.e., the stability of the earth throughwhich the working is being driven, the advance on the face and so on,although in the most difficult circumstances likely to be encountered itis nevertheless possible to create groups of three since this minimumconstitutes a particularly economical arrangement.

Rigid groups of three structures are indeed known; however in theseknown control systems there is no facility for preventing thesimultaneous advancing of the casing structures located at the junctionpositions between such groups when it is desired to arrange for onestructure in each of the groups to move or where the facility for thisis provided. The logic system in accordance with the invention, however,excludes this possibility. Consequently, as many groups as desired canbe provided in the seam and the requisite security against doublemovement at the junctions between groups is provided.

FURTHER FEATURES OF THE INVENTION It is known, in relation to the priorart control systems men tioned at the beginning, to employhydro-pneumatic control elements, so that consequently control systemsof pneumatic kind can be regarded as known. Although the logic system inaccordance with the invention could. basically be operated eitherelectrically or for that matter pneumatically and hydraulically, it isnevertheless the preferred course to use certain kinds of pneumaticsystems, i.e., systems of the kind which are insensitive to pressurepulses of the kind occurring underground.

A system of this kind is known. Considering control of the hydrauliccasing system, the advantage is then obtained of a very long operationallife in the elements of which the system is formed, this operationallife being measured in the order of 10 switching operations. Also,limitations on the component modules and switching operations which canbe resorted to, are avoided, i.e., limitations of the kind which areinherent in electrical control systems because of the safetyrequirement.

Pneumatic logic systems are available whose basic modules can carry outthe following logic function:

Using three such modules, a store can be built up which has a dominantinhibit function. The property of this store is that a signal appliedtemporarily to its information input is maintained at its output untilthe stored signal is inhibited (erased) by the application of anothersignal to the inhibit input, although in the case that both signals areapplied simultaneously to the information input and the inhibit input,no output signal appears, i.e., the store does not switch through.

In accordance with a further feature of the invention, the switchingoperations required are carried out using storage elements of this kindin that, at the input of each control system associated with itsrespective casing structure, two series-connected dominant inhibitfunction stores are arranged, of which the input store is supplied atits information input with the signal preparing the advance of thecasing structure and has its inhibit input taken to the output of thesucceeding output store, the output store having its inhibit inputsupplied with locking signals from the neighboring casing structures viaan OR-element, and its output supplying locking signals for theparticular neighboring casing structures and a starting signal for thecontrol system belonging to its own casing structure.

It is also convenient to arrange the circuit in such a fashion that thelocking signal produced by the control system associated with theparticular casing structure is applied to the inhibit side of the outputstore. The locking signal appears when the advancing phase hasterminated, or when it cannot be executed.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be carried intopractice in various ways but a practical example thereof will now bedescribed with reference to the accompanying drawings, in which:

mum

FIG. 1 is a sequence of schematic diagrams, the left-hand diagram in thetop row indicating a pneumatic module and the right-hand diagram itslogic function; in the row below is shown an assembly of the dominantinhibit function store from three of the modules illustrated in thetopmost row; and in the bottom row is shown an abbreviated symboldesignating the dominant inhibit function store and its logic function;

FIG. 2 schematically illustrates the locking circuit for three casingstructures locked together in accordance with the present example, whoseindependent, associated control systems have however for the greaterpart been omitted; and

FIG. 3 illustrates, in four diagrams succeeding one another from the topdownwards, an example of the advancing process taking place in the seamin the neighborhood of a largish exposed roof zone of irregular form.

FIG. 4 is an overall block diagram of a system according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the topmost illustration ofFIG. 1, at the right-hand side is shown the logic function of a basicpneumatic module shown on the left-hand side. This basic module is inthe form of a pneumatically operated double-diaphragm valve 1. Twodiaphragms 3 and 4 are accommodated in a housing 2 and these diaphragmsare rigidly connected together at 5. Each diaphragm is associated withan annular gap 6 or 7 as the case may be, created by the provision of aninsert, and the annular gaps control the entry of air into the insert 8or the discharge of air therefrom across x The result is a total of foursignal connections marked x, to x and y. The number of inputs of thedouble-diaphragm valve 1 is indicated in the right-hand illustration,representing the logic combination.

Using three double-diaphragm valves of this kind, what is known as adominant inhibit function store can be constructed. This is illustratedin the central row of FIG. 1. Since the combining lines to the fiveconnections of each diaphragm valve 1 have been indicated and marked attheir ends, it can be seen that the logic circuit of the store containsa signal input, an inhibit signal input and a signal output, and twoadditional lines have to be provided one of which serves an airbleedfunction and the other to apply a pneumatic auxiliary medium.

In the bottommost row of FIG. 1, this dominant inhibit function storehas been schematically illustrated on the left, the designations of theconnections having been simplified, i.e.,

x,,= signal input x, inhibit input y signal output.

The logic combination of the inputs and the output is indicated at theright-hand side in the bottommost row of FIG. 1. It can be seen fromthis that the dominant inhibit function store has the followingproperty:

If a signal is applied to x, for a short time only, a signal ismaintained at the output y until an inhibit signal appears at XL. On theother hand, if signals x, and x are applied simultaneously, then no ysignal appears, i.e., the store does not switch through.

The illustration of FIG. 2 must be imagined as continuing to both sides.The result is a logic circuit for covering all the casing structures atthe seam in a mine working. In the circuit shown in FIG. 2 as anexemplary embodiment, in each case one casing structure, e.g., II, islocked to the other two, tag, I and Ill. The casing structures can takethe form of trusses, i.e., frameworks, which are linked together by feedcylinders, but may equally well be in the form of in-line frames,pit-props or individual frames, which are connected to the conveyor.

Each of the casing structures or frames is equipped with its own controlsystem including at least one element which measures the distanceadvanced, in particular a sensing device cooperating with the roofand/or sill of the seam. Sensing devices of this kind are well known andtherefore require no particular explanation here. Using these sensingdevices, the

control system can be set into readiness for the advancing movemen orcan be locked.

In accordance with FIG. 2, at the input of the control systems (notshown in any detail) there are in each case two series-connecteddominant inhibit function stores 101 and 102, or 201, 202, or 301, 302.The input stores are those marked 101, 201, and 301, whilst thesucceeding output stores are those marked 102, 202 and 302.

Since, at this stage, the logic system in question has now beendescribed in relation to each casing frame, we will now confineourselves to a discussion of the system associated with casing frame II.The corresponding systems of casing frames I and III are givencorresponding references.

The input store 201 is provided at its information side (signal input)with a line 204 which carries the signal preparing the frame for anadvancing movement. The preparing signal is produced by the sensingdevice hereinbefore referred to. The inhibit side (inhibit input) isconnected to a line 205 which leads to the output (signal output) 206 ofthe succeeding output store 202. The output store 202 has its inhibitside 207 connected through an OR-element 203 to lines 208, 209 in whichlocking signals appear, and emanating from the neighboring casingframes. The output 206 is also connected to a line 210 which, throughlines 211, 212, supplies locking signals to the casing frames I and III.Finally, a line 213 supplies a signal coming from the control system ofthe casing frame itself and appearing at the end of the advance movement(or in the event that a prescribed advance is impeded). This line 213also leads to the OR-element 203 andthus to the inhibit side of theoutput store 202.

From the line 206, i.e., the output 206 of the dominant inhibit functionstore 202, a line 214 leads to the control system of the relevant casingframe, in which line the advance command triggering the control systemappears.

Any signal indicative of permission to advance, which comes from thesensing device and appears on say the line 204 at the signal input ofthe store 201, is stored in the store 201 until the locking signals,applied by the OR-element 203 to the inhibit input 207 by theneighboring casing frames I and III, are suppressed. Then, the dominantinhibit function store 202 switches through and carries out thefollowing operations:

First ofall, through the line 214, the command advance" is passedthrough the line 204 to the control system of casing frame II. At thesame time, the signal on the line 204 is erased through the line 205leading to the dominant inhibit function input store 201. Also, throughthe lines 212 and 211, locking signals are applied to the inhibit sideof the dominant inhibit function stores 103 and 303 of the neighboringcasing frames I and III.

As soon as the casing frame 11 has ceased its advancing movement, thereappears on the line 213 a signal which inhibits the signal on the line214. This cancels all the locks hitherto produced by the casing frameII.

By departure from the logic circuit illustrated and describedhereinbefore in detail, it is also possible to determine the sequence inwhich the locks on the neighboring casing frames I and III arecancelled. This can be effected by signal-delay elements (throttles andvolumes) incorporated into the locking lines 21 l, 212, or by additionaldominant inhibit function stores, inserted between 201 and 202 andhaving corresponding locking lines. Furthermore, it is possible in thisway to provide facility for modifying (during operation), the grouplength which is determined by the locking lines, this for example byswitching from an interlock of three" arrangement to an interlock offive arrangement.

This means that, when a casing frame has finished its advancingmovement, one or other of the casing frames I and III, or casing frameswhich are not immediately adjacent but which are interlocked, willadvance.

The casing process which is produced, in the presence of an irregularlyexposed zone 500 of the roof of the working at a face 500a, isschematically illustrated in FIG. 3. Here, four phases can be detectedand these have been illustrated consecutively from top to bottom in FIG.3.

In order to simplify understanding, arrows are used in relation to thecasing frames to indicate which of the frames have been prepared foradvance, by their sensing devices, as explained hereinbefore. Arrows,above the rectangles depicting the casing frames, indicate that theparticular frame is advanc' ing and that the neighboring casing framesare locked.

In the example of FIG. 3, a total of ten casing frames 501 to 510 havebeen shown. The frames are grouped together in the manner indicated bythe circuit of FIG. 2, to form a logic system.

As soon as the casing frames 503 to 508 have been prepared for advance,the question of which of the frames then actually advances and locks theneighboring frames, is a matter determined by the switching rate. In thefirst phase, the casing frames involved are those marked 5G5 and 508. Assoon as the frames 505 and $08 advance, they lock their neighbors in theaforedescribed fashion so that the frames 503, 504 and 506, 507, whichare also in the prepared" condition, are prevented from advancing. Thecondition is then reached which is shown in the second illustration ofFIG. 3. The frames 505 and 508 have completed their advancing movementand, by unlocking the frames 5G7 and 509, as well as 506 and 504, haveleft the latter free to advance themselves. This facility is detected bythe frames 504 and 507. Accordingly, they have locked the frames 506 and508, as well as the frames 503 and 505.

In the third phase, therefore, the frames SM, 505, and 507 and 503, haveadvanced, so that the frames 503 and 506 can now feed forward and in sodoing lock the frames 502, SM, 505, 507, whilst the frames 501 and 508,509 and 510 are unlocked.

In a fourth phase, we have the condition shown in the bottommostillustration of FIG. 3, in which the roof exposed by the irregularworking ofthe face is completely cased.

FIG. lillustrates a control system in which the logic circuitry iscontinuing to both sides for operating a plurality of automaticallyadvancing casing structures 501 through 509. A plurality of controlsystems 115a, 215a, 315a, 115b, 215b, 315b, 1150, 215a, and 315v arearranged respectively to control casing structures 501 through 509. Thecontrol systems are arranged into a first group 115a, 215a, 315a, asecond group 115b, 215b, and 315b, and a third group 11150, 2156 and3150, each group comprising a circuit as described and illustrated inconnection with FIG. 2.

Associated with the respective control systems are sensing means 117a,217a, 317a, 117b, 217b, 317b, 117c, 217c, and 3170 for determining whenits associated casing structure is nominally free to advance.Transmission lines 113a, 213a, 3l3a, 113b, 213b, 313b, 1130, 213C, and313C are connected to provide input signals to the control systems fromthe sensing means. Transmission lines ll la, 2114a, 314a, 114b, 214b,314b, 1114c, 214C, and 314C provide output signals from the controlsystems respectively to motive means 116a, 216a, 3160, 116b, 2161;,316b, 116e, 216a and 3160 which operate to release and advance theassociated casing structures.

It will be seen that the logic circuit which groups together the variouscontrol systems associated with the casing frames gives rise to groupsof changing control which incorporate as many casing frames as isdetermined by the number of locking lines.

Finally, the prime advantage of the invention resides in the fact thatsmall groups can be produced and accordingly any exposed roof regionwhich may develop can be underpinned as soon as it occurs, This is apoint of extreme significance where the necessary supporting of theroofs of all mine workings is concerned. Since, moreover, the logicsystem is continually operative, corrections to roof support areeffected even when the extraction machinery is not working.

A substantial achievement of the invention resides in the fact that, atthe junctions between the groups, it is ensured that two neighboringcasing frames are inhibited from simultaneous advance. Consequently, atall times a selectable roof zone is exposed which is formed within thegroups by one casing frame only. It is possible in this way to preventthe seam from collapsing in the neighborhood of the cased roof of theworking.

A further advantage is the high advance frequency. If a casing frame isunable to advance because it is not receiving a signal from its sensingdevice, then it cannot lock and therefore another frame can immediatelymove, whereas with a fixed group system the next frame has to wait forthe particular signal intended for it.

I claim:

1. In a hydraulic casing system for working a mine seam comprising: aplurality of automatically advanceable casing structures, acorresponding plurality of motive means for advancing respective casingstructures, a corresponding plurality of sensing means for determiningwhen respective casing structures are nominally free to advance, acorresponding plurality of control systems for the respective casingstructures, and a plurality of transmission lines interconnecting saidsensing means and said motive means with said control means forpreparing said control systems when respective casing structures arenominally free to advance and for transmitting selective signals fromsaid control systems to respective casing structures to release andadvance the respective casing struc' tures,

the improvement comprising; means interconnecting the casing structuresand their associated control systems in groups for allowing only onecasing structure in any one group to be released and advanced at onetime, while several casing structures in different groups can bereleased and advanced simultaneously, said interconnecting meansincluding a logic system into which all the casing structure controlsystems are incorporated and which includes, for each such casingstructure control system, series-connected input and output dominantinhibit function stores, each of said stores comprising an informationinput terminal, an inhibit terminal and an output terminal, of which theinput store is provided at its information terminal with a signalindicating preparedness for ad vance, and at its inhibit terminal isconnected to the output terminal of the output store, the outputterminal of the output store producing locking signals for theneighboring casing structures as well as a starting signal for thecontrol system ofits own casing structure, the output store having itsinhibit terminal supplied through an OR gate with such locking signalsfed from neighboring casing structures.

2. A hydraulic casing system according to claim I, wherein the lockingsignal, supplied by the control system associated with the respectivecasing frame, is applied to the inhibit terminal of the output store.

3. In a hydraulic casing system for working a mine seam comprising: aplurality of automatically advancable casing structures, a correspondingplurality of motive means for advancing respective casing structures, acorresponding plurality of sensing means for determining when respectivecasing structures have open space into which to advance, a correspondingplurality of control systems for the respective casing structures, and aplurality of transmission lines interconnecting said sensing means andsaid control means for unlocking said control systems for operation whenthe corresponding casing structures have said open space andinterconnecting said control means and :said motive means fortransmitting selective signals from said control means to release andadvance respective casing structures,

the improvement comprising: means for interconnecting the casingstructures and their associated control systems in groups and forallowing only one casing structure in any one group to be released andadvanced at one time while allowing several casing structures inrespectively different groups to be released and advance-dsimultaneously,

said interconnecting means including fluid-operated logic means forautomatically causing, in any group, any otherwise uninhibited controlsystem to advance its casing structure immediately when that casingstructure has said Mum said interconnecting means includes, for eachcasing structure control system, series-connected input and outputdominant inhibit function stores, each of said stores comprising aninformation input terminal, an inhibit terminal, and an output terminal,of which the input store is provided at its information input terminalwith a signal indicating preparedness for advance, and at its inhibitterminal is connected to the output terminal of the output store, theoutput terminal of the output store producing locking signals for theneighboring casing structures as well as a starting signal for thecontrol system of its own casing structure, the output store having itsinhibit terminal supplied through an OR gate with such locking signalsfed from neighboring casing structures.

1. In a hydraulic casing system for working a mine seam comprising: aplurality of automatically advanceable casing structures, acorresponding plurality of motive means for advancing respective casingstructures, a corresponding plurality of sensing means for determiningwhen respective casing structures are nominally free to advance, acorresponding plurality of control systems for the respective casingstructures, and a plurality of transmission lines interconnecting saidsensing means and said motive means with said control means forpreparing said control systems when respective casing structures arenominally free to advance and for transmitting selective signals fromsaid control systems to respective casing structures to release andadvance the respective casing structures, the improvement comprising;means intercOnnecting the casing structures and their associated controlsystems in groups for allowing only one casing structure in any onegroup to be released and advanced at one time, while several casingstructures in different groups can be released and advancedsimultaneously, said interconnecting means including a logic system intowhich all the casing structure control systems are incorporated andwhich includes, for each such casing structure control system,series-connected input and output dominant inhibit function stores, eachof said stores comprising an information input terminal, an inhibitterminal and an output terminal, of which the input store is provided atits information terminal with a signal indicating preparedness foradvance, and at its inhibit terminal is connected to the output terminalof the output store, the output terminal of the output store producinglocking signals for the neighboring casing structures as well as astarting signal for the control system of its own casing structure, theoutput store having its inhibit terminal supplied through an OR gatewith such locking signals fed from neighboring casing structures.
 2. Ahydraulic casing system according to claim 1, wherein the lockingsignal, supplied by the control system associated with the respectivecasing frame, is applied to the inhibit terminal of the output store. 3.In a hydraulic casing system for working a mine seam comprising: aplurality of automatically advancable casing structures, a correspondingplurality of motive means for advancing respective casing structures, acorresponding plurality of sensing means for determining when respectivecasing structures have open space into which to advance, a correspondingplurality of control systems for the respective casing structures, and aplurality of transmission lines interconnecting said sensing means andsaid control means for unlocking said control systems for operation whenthe corresponding casing structures have said open space andinterconnecting said control means and said motive means fortransmitting selective signals from said control means to release andadvance respective casing structures, the improvement comprising: meansfor interconnecting the casing structures and their associated controlsystems in groups and for allowing only one casing structure in any onegroup to be released and advanced at one time while allowing severalcasing structures in respectively different groups to be released andadvanced simultaneously, said interconnecting means includingfluid-operated logic means for automatically causing, in any group, anyotherwise uninhibited control system to advance its casing structureimmediately when that casing structure has said open space into which toadvance, and with no predetermined sequence of allowing release andadvancement of the casing structures.
 4. A hydraulic casing systemaccording to claim 3 wherein the logic means has the additional functionof preventing the simultaneous advance of any two adjacent casingstructures.
 5. A hydraulic casing system according to claim 4 whereinsaid logic means comprises pneumatic combinational logic and datastorage elements.
 6. A hydraulic casing system according to claim 4wherein said interconnecting means includes, for each casing structurecontrol system, series-connected input and output dominant inhibitfunction stores, each of said stores comprising an information inputterminal, an inhibit terminal, and an output terminal, of which theinput store is provided at its information input terminal with a signalindicating preparedness for advance, and at its inhibit terminal isconnected to the output terminal of the output store, the outputterminal of the output store producing locking signals for theneighboring casing structures as well as a starting signal for thecontrol system of its own casing structure, the output store having itsinhibit terminal supplied through an OR gate with such locking signaLsfed from neighboring casing structures.